an overview of seabed surveys (high-resolution geophysical site
TRANSCRIPT
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An Overview of Seabed Surveys(High‐resolution Geophysical Site
Surveys)
Anna FulopChief Geoscientist Fugro Survey Limited
22 April 2015
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• Introduction• Site survey - purpose and requirements• Principles, Methods and Tools• AUV Surveys• Site Survey Operations• Interpretation and Presentation
Agenda
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Introduction - The Fugro Group
• Dutch multinational company; headquarter in Leidschendam, NL. • Fugro provides People, Equipment, Expertise and Technology worldwide;
Approximately 12,000 employees in over 60 countries.• Activities: acquire and interpret Earth’s surface and sub-surface data to
support the design, construction, installation, repair and maintenance of infrastructure, on land and at sea.
• 3 Divisions (Geotechnical, Survey and Subsea Services) each containing numerous individual Operating Companies (OpCos).
• Survey division: Oil & Gas industry, Renewables, Mining, etc
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Fugro Survey Division• Meteorology and oceanography,
Weather forecasting
• Offshore structural monitoring
• Marine environmental services
• Geophysical Survey, cable route and hydrographic survey
• Construction survey support• Satellite positioning, monitoring and
mapping
• Aerial mapping, Terrestrial surveying
• Geospacial GIS solutions
IntroductionFugro Survey Limited• High-resolution marine geophysical
site surveys (Oil & Gas industry) -seabed mapping, drilling hazard surveys, regional and deep-water surveys, pipeline route surveys
• Offshore positioning services and construction support - rig moves, pipelayoperations, etc
• Main office in Aberdeen
• Operate worldwide, but predominantly in NW European Continental Shelf (UKCS, NOCS, Dutch and Danish sectors), offshore West Africa
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A survey is required for anything that…• is moved from one place to another (e.g. rig
move, site clearance/abandonment)• is laid on the seabed (e.g. pipeline, power/
telecommunication cable)• has foundations in the seabed (e.g.
platforms, buried pipelines, wellheads, manifolds, anchors, offshore wind turbines)
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Site surveys - purpose and requirements
• might affect environmentally sensitive areas
• may be affected by geohazardsor offshore or fishing activity
… goes on or in the seabed
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A survey will determine:• Seabed conditions
- Bathymetry: water depth, gradients, relief- Seabed sediment types (clay, sand, gravel, bedrock)- Seabed obstructions (existing infrastructure, wrecks, debris, boulders,
UXO)- Potentially sensitive habitats (e.g. coral, herring spawning grounds,
MDAC)
• Sub-seabed conditions- geology - foundation / anchoring conditions - trenching conditions
• Potential Geohazards- Slope stability- Faulting- Probability of shallow gas
Are these conditions suitable and safe?
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Site surveys - purpose and requirements
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Seabed Conditions - Bathymetry
Iceberg ploughmarks, northern North Sea
Pockmark, central North Sea
Megaripples and spud can depressions, southern North Sea
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Seabed Sediments and Features
Sand with rock outcrop
Pipelines with associated infrastructure; soft clay with numerous pockmarks
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Seabed Sediments and Features
Unexploded Ordnance (UXO)
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Seabed Sediments and Features
Debris (cable / wire)
Abandoned telecom cable near proposed drilling location (not mapped)
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Environmentally Sensitive Habitats (DECC requirements in the North Sea)
Area of possible Coral on SSS data
Seabed photograph of Coral colonies
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Sub-seabed Conditions
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Geohazard Identification – Seabed Stability
Evidence of slope instability
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Geohazard Identification - Faulting
Evidence of faulting on 2DHR seismic data
500m
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Geohazard Identification – Potential Shallow Gas
500m
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What are the risks of not doing a site survey?
West Vanguard Blowout, NOCS (1986)
Punch-through
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Basic Principles• Use of geophysical ‘remote sensing’ techniques• Predominantly use acoustic methods
- Range of equipment and methods- Range of acoustic frequencies
• Calibrated by some limited ‘ground truth’ sampling- Geotechnical- Environmental
• Platform: dedicated survey vessels vs vessels of opportunity
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Principles, Methods and Tools
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Echo Sounders • Single and multibeam systems, generally hull-mounted
• Water depths measurements
• Topography
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SINGLE BEAM
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Side Scan Sonars• High, low, dual frequency towed systems
• Measure seabed reflectivity
• Detection / identification of seabed sediment and obstructions
• Measurement of dimensions (particularly height above seabed)
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Fine SAND
RippledSAND Boulders/
Clay outcrops
RippledSAND
Fine SAND
Side Scan Sonar Data – seabed sediments
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Side Scan Sonar Data – detailed mapping of seabed obstructions
Uncharted WRECKL=33m, W=6m, H=3.3m Acoustic
shadow
Seabed
Area of debris
Surface-laid pipeline
Anchor scarwith pit
Smalldepression
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High-resolution Seismic Systems• Used for sub-seabed mapping
• Seismic reflection
• Single-channel systems:- Pingers (generally hull-mounted)- Chirps (towed / hull-mounted)- Boomers / Sparkers (towed)- Single airguns (mini gun and single channel streamer)
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High-resolution Seismic Systems (cont’d)• 2D high-resolution multichannel seismic
- typically 140 cu.in. sleeve airgun source fired at 6.25m / 12.5m intervals
- 48 / 96 channels, 600m / 1200m hydrophone streamer- Digital recording system- Extensive data processing required- Deeper penetration and increased signal / noise ratio
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Summary of Acoustic Methods
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Other Tools and Survey Methods• Complement the acoustic geophysical
survey data • Magnetometer, Gradiometers• Geotechnical testing/sampling
- Grab sampler- Gravity / Piston Corer- Vibrocorer- Cone Penetrometer Testing (CPT)- Deep boreholes (>30m bsb)
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Other Tools and Survey Methods (cont’d)• Environmental Surveys
- Underwater camera: sills and video transects- Box coring
• Have become standard part of most seabed surveys
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AUV Surveys – Deep Water Solution
• Traditional survey methods have numerous drawbacks to the acquisition of geophysical data in deep water areas:
- Deployment / recovery difficult in bad weather conditions- Noise / weather effects, vessel motion- Limited penetration and data resolution (hull-mounted systems)- Sensor positioning imitation (acoustic positioning for towed sensors)
• For deep water areas, better resolution and better positioning are needed
• The survey industry’s solution: The Autonomous Underwater Vehicle (AUV)
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Fugro’s “Echo Surveyor IV” AUV
• Kongsberg HUGIN 1000• Semi-autonomous vehicle
independently powered and controlled (cable free).
• Depth rated to 3000m.• Aided Inertial Navigation System
provides extremely accurate positioning.
• Positional accuracy of the AUV is less than 5m, significantly better than towed systems.
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Improved bathymetry data quality
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Bathymetry from 3D seismic data
AUV mounted multibeam echo sounder data
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Improved sub-bottom profiler data quality
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2DHR Data AUV Chirp Data
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Improved seabed imagery quality…
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With option to mosaic images
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Onshore• Vessel PM, main point of contact
between survey vessel and client
• Geoscience Team Leader
Site Survey OperationsOffshore – Full Survey Team• 24 hour operations
• 1 Party Chief
• 2 Online Surveyors (Day/Night)
• 1 Technical Coordinator
• 4 Engineers (Day/Night)
• 1 QC Geophysicist
• 1 Environmental Scientist
• Optional requirements:2nd Geophysicist, Processing surveyor, Seismic processor, Gun mechanic, Geotechnical survey crew
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Data interpretation• Variety of software used for the different datasets
• Large volumes of data handled
• Integration of all available data essential – suitable software required
Final Product – Site Survey Report
• Comprehensive, structured and high-quality survey report
• Often includes integrated geophysical, environmental and geotechnical results
• Detailed figures and charts showing the final interpretation
• Digital deliverable (CAD files, GIS deliverables)
Interpretation and Presentation
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• Geophysical site surveys are essential to ensure the suitability and safety of sites for offshore infrastructure construction
• During a site survey a large amount of information on the seabed and sub-seabed environment is acquired
• A detailed and integrated interpretation is required to turn this information into a high quality site survey report for the end user
• The requirements vary from project to project; techniques, data quality and level of interpretation have to match these requirements
Summary
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Thank you
Any Questions?